Dual-isotope ratios of carbonaceous aerosols for seasonal observation and their assessment as source indicators.

Carbonaceous aerosols exhibit seasonal variations due to a complex interplay of emission sources, meteorological conditions, and chemical processes. This study presents the first year-round dual‑carbon isotopic analysis of carbonaceous aerosols in Northeastern Europe (Lithuania). The emphasis was placed on the processes affecting carbonaceous submicron particle (PM ₁ ) concentrations and their isotopic composition (δ ¹³ C _TC , f _c ) during different seasons. Aerosol particles were collected in the two distinct sites: at an urban background site (Vilnius) and a coastal site (Preila). The concentrations of total carbon (TC) and black carbon (BC) varied both spatially and temporally. The annual average concentrations were 4 μg/m ³ for TC and 2.3 μg/m ³ for BC at the urban background site. They were considerably lower at the coastal site with 2.9 μg/m ³ for TC and 0.74 μg/m ³ for BC. The peak concentrations of TC and BC that occur during the cold season indicate a significant impact from residential heating. The δ ¹³ C in aerosols exhibited a distinct seasonal cycle with depleted δ ¹³ C _TC values during the warm season (April-October). Through the integration of isotopic composition, contemporary carbon (f _c ), and BC source apportionment, we achieved precise predictions of isotopic parameter changes, encompassing pollution sources and the influence of meteorological parameters. To better understand the respective contributions of local and regional sources, air mass trajectories, wind patterns (speed and direction), and the polar conditional probability function (CPF) were studied in parallel. The study indicates that the isotopic composition of PM ₁ at both sites is primarily controlled by emission sources (local and regional), while meteorological conditions (temperature and mixing layer height) have less influence. These variations have important implications for regional air quality, climate dynamics, and public health, which are persistently subject to continuous research and monitoring.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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